Photopolymerizable organopolysiloxane compositions containing SiC-bonded acryloxyalkyl or methacryloxy groups and mercaptoalkyl groups are described in U.S. Pat. No. 4,290,869 to Pigeon. These compositions are stable in closed and opaque containers, for about 48 hours. (See column 8, lines 36 to 38).
Photopolymerizable organopolysiloxane compositions containing SiC-bonded thioacryloxyalkyl and mercaptoalkyl groups are also described in U.S. Pat. No. 4,359,369 to Takamizawa et al.
The organopolysiloxanes of this invention differ from the organopolysiloxanes described in U.S. Pat. No. 4,290,869 in that they are substantially free of SiOC-bonded organic radicals. It is believed that this contributes to the better storage stability of the organopolysiloxanes of this invention. Furthermore, it is surprising that the organopolysiloxanes of this invention rapidly crosslink when exposed to high-energy radiation in the absence of the SiOC-bonded organic radicals.
Therefore, it is an object of the present invention to prepare readily available organopolysiloxanes which can be stored for at least 6 months in closed and opaque containers at ambient temperature. Another object of the present invention is to provide organopolysiloxanes which do not emit an unpleasant odor. Still another object of the present invention is to provide organopolysiloxanes which rapidly crosslink when exposed to high energy radiation. Still another object of the present invention is to provide organopolysiloxanes which readily crosslink in the presence of atmospheric oxygen when exposed to high energy radiation without noticeable post-crosslinking. A further object of the present invention is to provide organopolysiloxanes in which the "release-value" of the coatings either prior to or after crosslinking remains essentially the same over a long-term storage period. A still further object of this invention is to provide crosslinked organopolysiloxane coatings which are very transparent, flexible and abrasion-resistant.